Amplifier control circuits



April 13, 1943 J. VAN sLoo'rEN y|:r AL 2,316,474 y AMPLIFIER CONTROLCIRCUITS Y Fileduay s, 1940 EXPANSION A cour/20L TUBE ,4J-1A PL. l i

25 C 0L)- v v U5 70A F 27 33 l I J l lNvEN-roR l 35 JACOB ww swarm lBERNARQUS mmnlnfusc//ENAU BYyTSg ATTORNEY Patented Apr. 13, 1943 l2,316,474 AMPLIFIER co'N'raoL CIRCUITS Jacob van Slooten and BernardusW. van Ingen Schenau, Eindhoven, Netherlands, assig'nors to Y RadioCorporation of Delaware Application May 3,. 1940,' Serial No. 333,080

of America, a corporation In the Netherlands Septemberll, 1939 'ZQlaimS.

This invention relates to a circuit for generating or amplifying acontrolvoltage. Control voltages are used in circuits for amplifyingand/or selecting a frequency-band. Thus, for example, a control voltagepermits of controlling the amplification of a circuit of this characterso as to -be at least substantially inversely proportioned to the inputvoltage supplied to the circuit. This is the so-called automatic volumecontrol which is used with radio receivers. In this case the value ofthe control voltage depends on the intensity oi' the input voltage whichis to be amplified. As an alternative, in a circuit serving ier theselective amplication of a fre,- quency hand a control voltage may beused for controlling the selectivity of the circuit, for example, inaccordance with interfering, adjacent channel voltages.` in such acircuit control voltage may also he used for correcting tuning, thevalue of theV control voltage depending on the divergence between thereceived frequency band and the frequency to which the receiver istuned.

Both thelatter controls are known with wireless receivers 'as Jautomatieband Width` control c the control voltage has to he derived with the aidof a diode, so that a negative control voltage y, relative to earth, towhich the diode cathode is generally connected, is set up.

circuits for the use of a positive control voltage have to be' used, orpositive control voltage has to be derived which after amplificationresults in a negative control voltage. This, however, entails thedisadvantage that the'diode cathode K Vis not connected to earth.

According tothe invention the'above mentioneddifculties are obviated dueto the fact thatthe circuit comprises a tube having at least one controlgrid, one auxiliary cathode emitting secondary electrons and one anode,to the control grld of which the control voltage to be amv pliiied, or avoltage from which the control volty age is derived, is supplied andfrom theauxilgenanoole detector and supplying a low frequency signalvoltage to the control grid a positive cony. trol voltage for contrastexpansion can be obtained at the auxiliary cathode. The advantage ofthiscircuit is that a supplementary tube for En the part ci? thespecication following here'- l inaiter a negative, or positive, controlvoltage is intended to mean avcltage which is lower or higherrespectively than the voltage which is set up when the signal voltagefrom which the `con-- `-vfreverslrig the polarity of the control Voltagei can be: economized. t Y. In order that the invention may be clearlyunderstood and readily carried into eiect it will now be described morevfully with reference to the accompanying drawing, in which Fig. i showsa circuit for automatic volum control Vwith amplied control voltageaccording to the invention, l

Fig. 2 shows a modication wherein the tube for amplifying the controlvoltage also serves as a. llow frequency ampliiler valve.

Fig. S shows a circuit arrangement of a low The use of such a tubeoffrequency amplifier Lwith contrast vexpansion according to theinvention. i

Innlilg. l an intermediate frequency (I. F.) amplifier stage and adiodedetector of asuperketerodyne lradio receiver are shown.` lTheintermediate frequency oscillations occurring inv an intermediatefrequency' circuit l are amplied by an amplifier valve 2 and supplied toan a intermediate frequency vcircuit 3 which, jointly with anintermediate frequency circuit 4, forms a bandpass/ filter. Theintermediate frequency voltage which occurs across the circuit 4v isrectiiied by a rdiode 5, and with the interposition of a resistanceSshunted by a condenser 1, supplies a direct control voltage upon whichthe low frequency oscillations are superposed. The low frequency voltageis supplied to a low frequency amplier (not shown) by a contact 8slidable on the resistance 6 and a condenser 9. l.

'I'he negative control voltage occurring across the resistance 6 issupplied by a resistance I0 to the control grid II of a valve I2. Thevalve I2 comprises an auxiliary cathode I3 which, upon bombardment byelectrons, emits secondary electrons which move to an anode I I. Theauxiliary cathode I3 receives a positive voltage through a resistanceI5, and is' connected to earth by a condenser I6 which has a negligibleimpedance. 'Ihe auxiliary cathode I3 is connected to the control grid2Il of the amplifier valve 2 through the conductor I'l and resistanceI8.

When feeble signals are being received the diode supplies only a smallnegative direct voltage so that an intense flow of electrons flows inthe valve I2 from the cathode to the auxiliary cathode I3. Thus, theauxiliary cathode emits a lot of secondary electrons so that thepotential of the auxiliary cathode is higher than the potential of theend I9 connected to the positive terminal of the source of voltagesupply (not shown), of the resistance I5. The control grid of theamplier'valve 2 has the same potential as the auxiliary cathode I3, andthe cathode 2| of the valve 2 has a slightly higher positive potentialrelative to earth due to its being connected to a point of apotentiometer 22 connected between earth and the positive terminal of asource of voltage supply.

In the case of feeble signals the valve 2 has a low negative gridvoltage and a high amplification. being received the control grid II ofthe valve I2 is highly negative. Little current flows to the auxiliarycathode I3 and the potential of the auxiliary cathode I3 is onlyslightly more positive than .the potential of the point I9.Consequently, the potential of the control grid 20 is, also, lesspositive than'with feeble signals so that the valve 2 has but a lowamplification. Referring to the drawing, the automatic volume control(AVC) is only effected on the valve 2. The auxiliary cathode I3 may,however, be connected to the control, or regulating, voltage grids ofone, or more, .preceding valves (not shown) also with the interpositionof resistances.

Referring to Fig. 2, in which similar parts are designated by likereference numerals, the valve I2 is also used as a low frequency, oraudio, amplier valve. 'Ihe control grid II has supplied to it thecontrol voltage to be amplied through a resistance I0, andthe lowfrequency alternating voltage to be amplified is f'ed through thecondenser 9. Similarly to Fig. 1 the amplified control voltage isobtained from the auxiliary cathode I3. 'I'he ampliiled low frequencyvoltage is supplied to the low frequency I'amplifier (not shown) by acondenser 23. 'I'he anode circuit of the valve I2 comprises a resistance24.

Fig. 3 shows the nal stage of a low frequency 6 amplier employingcontrast expansion. The terminals and 28 have supplied to them audiovoltage. -The terminal 23 is connected to the control gridv'of a valve21, which comprises an auxiliary cathode 23, and to the grid of anamplifier valve 29, the anode circuit of which includes the primary of aloudspeaker transformer 30. A loudspeaker 3| is connected to thesecondary of the said transformer.

If, on the contrary, powerful signals are 'is adjusted as ananodedetector.

tains a screening grid 32. The terminal 26 is earthed.

The low frequency voltage which occurs between the terminals 25 and 26is amplified by the valve 29 and supplied to the loudspeaker 3l. Theamplification of the valve 29 depends on the potential of the screeninggrid 32. This screening grid is connected, jointly with the auxiliarycathode 28 of the valve 21, to a point 36,01 a potentiometer 35, andhas, therefore; the same potential as this auxiliary cathode. Thecathode 33 of the valve 21 is connected to such a point of thepotentiometer 34 that the valve 21 -The flow of electrons passing fromthe cathode `33 to the auxiliary cathode 28 is consequently dependentupon the value of the low frequency voltage which occurs between theterminals 25 and 26. In the case of a high voltageV much current, and inthe case of a low voltage little current, flows to the auxiliarycathode. At high voltage the potential of the auxiliary cathode 28, andthus the potential of the screening grid 32, is high so that theamplification of the valve 29 is also high; In the case of lower audiovoltages on the contrary the amplification of the valve 29 decreases.'Ihis results in contrast expansion. The advantage of the use of a valvecomprising an auxiliary cathode for the generation of the controlvoltage required for contrast expansion resides in the fact that a diodeand a separate reversing tube can be omitted.

What is claimed is:

ll. In combination with a signal voltage amplifier tube. meansresponsive to signal amplitude variation for controlling the gain of theamplilier, said responsive means including a tube having at least anelectron emission element, a plate, a control electrode and4 a secondaryelectron emission electrode arranged adjacent the path of electronsflowing from said element to said plate, a direct current voltagecontrol connection from the secondary emission electrode to saidamplifier, and means for applying signal-representative voltage to saidcontrol grid.

2. In combination with a signal voltage ampliiler tube, means responsiveto signal amplitude variation for controlling the gain of the amplifier,said responsive means including a tube having at least an electronemission element, a plate, a control electrode and a secondary electronemission electrode arranged adjacent the path of electrons flowing fromsaid element to said plate, a direct current voltage control connectionfrom the secondary emission electrode to said amplifier, and means forapplying signalrepresentative voltage to said control grid. said lastmeans including a rectifier of signals applied to said amplifier, and adirect current voltage ininection between said rectifier and control 3.In combination with a signal voltage amplier tube, means responsive tosignal amplitube having at least an electron emission element,

` a plate, a control electrode and a secondary electron emissionelectrode arranged adjacent the path of electrons flowing from saidelement to said plate, a direct current voltage vcontrol connction fromthe secondary emission electrode to said amplifier, and means forapplying signalrepresentative voltage to said control grid, saidamplifier being an audio ampliiler. a source of The Valve 29 00n- A715audio signal voltage for the amplifier. said amplitier having anauxiliary gain control electrode in addition to input and outputelectrodes, and said control' connection being made to said auxiliary.gain control electrode.

4. In combination with a signal voltage amplifier tube, means responsiveto signal amplitude variation for controlling the gain of the amplifier,said responsiveV means including a tube havmeans impressing the detectedsignal voltage upon said control grid and means for deriving amplifleddetected signal voltage from the plate of ing at least ari-electronemission element, a plate,-

a control electrode and a secondary electron e' emission electrodearranged adjacent the path of electrons flowing from said element tosaid plate, a direct current voltage control connec` tion from thesecondary emission electrode tol said ampliiier, and means for applyingsignalrepresentative voltage to said control grid, said amplier havingsignal voltage input and output electrodesand said control connectionbeing made to an/'ut electrode of said amplifier.

5. lin/combination with a signal voltage amplier'ytube, means responsiveto "signal amplitude yvariation for controlling the gain of theamplilier, said responsive means including a tube having at least anelectronemission element, aplate, a control electrode and a secondaryelectron emission electrode arranged adjacent the path of electronsflowing from said element to said plate,

said control tube.

6. In a system ofthe type having a signal source, an amplifier for thesignalsl and means for utilizing amplified signals, thevxnethod ofautomatically controlling the gain of the amplifier which includesgenerating a stream of privV mary electrons or a predeterminedintensity. producing a stream of secondaryelectrons with said nfirststream, deriving a direct current voltage from said secondary electronstream, applying 'said derived voltage to said amplifier to control thegain thereof, and regulating the intensity of the gain thereof,regulating the intensity of said a direct current voltage gain controlconnection from the secondary emission` electrode to said amplifier, andmeans for applying signal-representative voltage to said control grid,asource of modulated carrier signal voltage coupled to the amplifierinput electrodes, a. detector coupled to said amplier output electrodesand providing detected signal voltage, said applying said rst stream inresponse to amplitude variations in said signals by rectifying signalsampliiied by said amplifier and applying the rectied signal voltage toregulate said first stream intensity and deriving amplified rectifiedsignals from said primary electron stream.

JACOB VAN SLOOTEN. BERNARDUS W. VAN INGEN SCHENAU.

